As Vaccines Roll Out, Will Risky Behavior Increase?

man holding coronavirus vaccine

Mar. 4, 2021 — With distribution of COVID-19 vaccines ramping up, and President Joe Biden promising all U.S. adults will be able to get inoculated by the end of May, many Americans are finally anticipating the end of the pandemic.

But Arthur Caplan, PhD, a bioethicist at NYU Langone Medical Center, sees the beginning of a new potential hazard: the Peltzman effect. University of Chicago economist Sam Peltzman first described the phenomenon decades ago when he observed that increased safety regulations had no effect on the highway death toll. It seemed people adjusted their behavior to take more risks as they perceived that a situation or threat became safer.

The Peltzman effect may spell bad news for the pandemic, Caplan and Brit Trogen, MD, a pediatric resident at NYU Langone, propose in a recent commentary.

“People seem to settle down to [be comfortable] with a certain amount of risk,” Caplan says. “And different people accept different levels of risk. When you offer them something that seems to reduce that risk, they often increase risk in other areas of their lives.”

As of March 2, according to the CDC, more than 26 million U.S. adults, or about 10% of the adult population, had received two doses of COVID-19 vaccines.

Once people are vaccinated, one of their first thoughts might be: “I’m due more fun,” Caplan says. So they might head indoors to restaurants or travel, despite the fact that much is still unknown about how variants of the coronavirus might change the course of the pandemic, or even whether a vaccinated person can still transmit the virus.

Peltzman Effect Factors

A classic example of the Peltzman effect in action is if someone drives a car faster after getting new brakes, knowing good brakes will decrease the chance of a crash. Another example implicates the safety of others: One study found that drivers passed more closely to bicyclists wearing helmets than those not wearing them, though those results have been questioned.

Those who study the Peltzman effect cite four things that influence whether risky behavior will increase once a situation appears safer. All four are present with the pandemic, Caplan says.

  • The new measure making the situation safer — in this case, the vaccine — has to be visible. It’s hard not to notice a jab in the arm, or the long lines for inoculation.
  • People must be motivated to engage in a risky or previously risky behavior. After a year of lockdown, many are.
  • People must have the control or ability to increase risky behavior. That’s easier in some states than others, with some lifting mask mandates and reopening businesses.
  • The new safety measure has to be effective enough that people are comfortable doing what they used to perceive as risky. The new vaccines, with up to 95% effectiveness, meet that measure.

What’s the Answer?

Caplan suggests the new public health message has to be clearer and more specific than previous communication so that the likely increase in risky behavior doesn’t put us back to high COVID rates.

People need to be told what kind of cautions they should still follow, like wearing masks and distancing, until more of the population is vaccinated, he says, and researchers get more answers on whether vaccinated people can still spread the virus. The CDC may soon issue guidelines on safe activities for fully vaccinated people.

People also need specifics about gatherings, Caplan says, such as, “If you are going to have a party, have it only with other vaccinated people.” Grandparents need specifics about whether it’s safe to visit grandkids and how to handle those visits — with masks or not?

What’s risky in one community may not be so in another as situations change, says Trogen. “We will increase or decrease our personal preventive behaviors based on the perceived riskiness of the virus,” she says.

As the number of vaccinated people increases, a misplaced sense that there is protective “herd immunity” may increase, Caplan says, “long before widespread immunity is truly present.”

His bottom line: Reducing risk, not eliminating it, should be the goal when easing safety precautions. But even if risky behaviors increase, as he expects, the change can’t counteract entirely the safety the vaccines provide.

“There will be more risky behaviors, such as less mask wearing, and more of all the activities that were cut back, pre-vaccine,” agrees Peltzman, who reviewed the paper. But will cases go back up? His prediction: “There will be more cases than if there was no ‘offsetting’ behavior.”

He, too, says public health messages are important and should focus on vaccination efforts. “The incentives for more risky behavior will not go away by telling people what is risky,” Peltzman says. “The likelihood of offsetting [risky] behavior makes widespread vaccination even more important.”

WebMD Health News


Sam Peltzman, PhD, Ralph and Dorothy Keller distinguished service professor of economics emeritus, Booth School, University of Chicago.

Arthur Caplan, PhD, bioethicist and Drs. William F. and Virginia Connolly Mitty professor, NYU Langone Medical Center and School of Medicine, New York City.

Brit Trogen, MD, pediatric resident, NYU Langone Medical Center, New York City.

Journal of Political Economy: “The effects of automobile safety regulation.”

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